1. Field of the Invention
The present invention relates to fiber optic networks, and more particularly, to monitoring the performance of fiber optic networks.
2. Description of the Related Art
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. As the traffic on fiber optic networks increases, monitoring and management of the networks become increasingly more significant issues. To monitor the network, the spectral characteristics of an optical signal at particular points in the network are determined and analyzed. This information may then be used to alter the performance of the network if the signal characteristics are less than optimal. Real time monitoring of this information is also important during setup and reconfiguration of the network.
FIG. 1A illustrates a bi-directional, wavelength division multiplexed (WDM) optical network 100 which utilizes an optical performance monitor (OPM) assembly 130 between a first node 120 and a second node 140. The multichannel optical network 100 comprises banks of light sources 105a,b which provide the light carrier wavelengths upon which the signals are modulated. These light sources, each occupying a different channel, are combined into a single optical fiber through a fiber-optic multiplexer (not shown). The signals then travel along optical fibers 110a-d between the two nodes 120,140. Each carrier wavelength, or channel, carries one signal in the WDM system. The totality of multiplexed signals carried by the optical fibers 110a-d in each direction is herein referred to as a composite signal. Occasionally, the signals have to be amplified by optical amplifiers 125a,b, such as Erbium Doped Fiber Amplifiers (EDFAs) or Raman amplifiers, due to attenuation of the signal strength. Typically, an optical signal is amplified after it travels approximately eighty kilometers or fifty miles.
The OPM assembly 130 may be located at various locations within the network 100 for the purpose of monitoring the characteristics of the optical signal so that the performance of the optical components of the network 100 may be determined. In one example, optical taps 115a,c are located proximate to respective upstream ports of the optical amplifiers 125a,b and optical taps 115b,d are located proximate to respective downstream ports of the optical amplifiers 125a,b. Providing upstream 115a,c and downstream taps 115b,d for the OPM 130 proximate the optical amplifiers 125a,b allows the OPM assembly 130 to measure the composite signal on either side of the optical amplifiers 125a,b and monitor the performance of the optical amplifiers 125a,b. Alternatively or in addition to monitoring the optical amplifiers 125a,b in the network 100, the OPM 120 may be used to monitor add/drop stations 135a,b in the network 100 as illustrated in FIG. 1B.
Typically, manufacturers offer only a single-port OPM 130a. In order to allow the single-port OPM 130a to accommodate a line from each of the taps 115a-d, a 4×1 optical switch assembly 130b is provided. The 4×1 switch assembly 130b includes a mechanical switch 130c-f for each of the four lines. Typically, these switches 130c-f are actuated continuously cycling through all input ports on the order of once per second. In order to have an acceptable service lifetime on the order of ten to twenty years, the switches need to endure about one billion cycles. Conventional mechanical switches, however, typically fail after about a million cycles. Therefore, frequent replacement of the mechanical switches is necessary.
As the foregoing illustrates, there exists a need in the art for a more reliable switch assembly for an OPM.